Utilizing a visible-light laser pointer to designate a position on a display is a known means for providing input to a control device such as a computer. For example, a display, such as an image projected on a screen, may include particular command areas, viewable by the user, and corresponding to particular commands. A camera is directed toward the display to provide image information to a computer, or controller. Thus, when a user directs a visible-light laser beam toward the display, specifically toward a particular command area, the controller can compare the projected image and the detected image to determine the difference between the two images, which corresponds to the location on the display where the laser beam strikes the display. If the laser beam is striking one of the command areas, the controller can execute a command associated with the command area. An example of such a command is to change the image on the display. Such devices are limited to referencing laser beam position on projected images only. The projected image must be stored within the controller for comparison with the laser-modified image. Such devices are not capable of determining a position of a laser spot on a surface wherein the unaltered image of the surface is not stored within the controller.
Another known input device determines the location of an infrared laser beam striking a display by utilizing an infrared camera in fixed relative position to the display. The infrared camera sends an infrared video signal to an image processing unit to digitize the video signal to determine the location of the infrared laser spot on the display. In addition, the device has the capability of sensing the location of multiple lasers pointed at the display simultaneously. Each laser may have a particular shape (e.g., three spots, a plus sign), also detectable by the infrared camera, such that a particular cursor associated with each particular pointer may be imaged upon the display in a position corresponding to the location of the particular laser pointer. Such devices are limited to circumstances wherein an infrared camera may be placed in fixed relation to the display for the determination of the absolute position of the laser spot on the display.
Yet another known device eliminates the camera of the above-noted examples and utilizes a detector located on the axis of an image projector. The device collects light from each on-screen pixel via a single detector during a scanning procedure, whereby the value of each pixel is collected individually, utilizing a pivoting mirror. During scanning, the detector can determine the presence and location of a spot illuminated by the laser pointer. Like the previous devices, such a device is useful for determining the location of an illuminated spot within a projected image, but is not useful in determining the location of an illuminated spot on any surface.
Another known input device utilizes a pen-shaped device for use with a patterned writing surface for detecting the location of the device with respect to the patterned surface. The patterned surface includes features that reflect light, such as infrared light, whereas the remaining areas of the patterned surface do not reflect such light. For example, the stylus includes an infrared light-emitting diode for projecting infrared light onto the patterned surface and a sensor sensitive to infrared light for detecting infrared light reflected by the features of patterned surface. Thus, when the device projects infrared light over a particular area of the patterned surface, the sensor detects a reflected sub-pattern of the patterned surface, which corresponds to the position of the device with respect to the patterned surface. By processing this sub-pattern, the location of the device with respect to the patterned surface may be determined. By determining this location, the location and movement of the device over the surface may be determined. Such a device is useful for handwriting recognition, for example, because the device must abut against, or be held a short distance from, the patterned surface in order to determine the position of the device. But such a device is not generally useful for pointing to a location on a patterned surface remote from the device some distance.